Printing machines for corrugated board sheets in use are divided into three types: printer-slotter machines for use with a highly viscous slow-drying glycolic ink, flexographic machines for use with a quick-drying aqueous ink of low viscosity, and printing machines previously proposed by the present applicant (JP-A No. 183549/1991) for use with a quick-drying glycolic ink which is nearly as low as the flexographic printing ink in viscosity. FIG. 9 is a side elevation schematically showing the printing machine proposed by the applicant. The machine has the advantages of both the printer-slotter press and the flexographic press.
The printing machine of FIG. 9 comprises an anilox roll 1 having minute indentations over the entire roll surface and movable into and out of contact with a printing die mounted on a plate cylinder 2, and an ink spray device 4a opposed to the anilox roll 1. A doctor blade 31 extending along the entire length of the roll 1 is in bearing contact with the roll 1 at an angle so as not to be opposed to the direction of rotation of the roll 1. A corrugated. board sheet 20 is nipped between and transported by the plate cylinder 2 and an impression cylinder 25 positioned under the plate cylinder 2.
The ink spray device 4a sprays the ink directly onto the anilox roll 1, and the ink dripping from the roll 1 is received by the doctor blade 31. The ink is sprayed onto the anilox roll 1 in a minimized quantity required to diminish the amount of ink remaining in the ink fountain 30 on the doctor blade 31 and to be discarded uselessly.
FIG. 10 is a side elevation showing a modification of the above machine. The modified machine has an ink squeezing rubber roll 3a opposed to the anilox roll 1 in contact therewith, and a doctor blade 3b bearing on the rubber roll 3a. The ink is supplied from an ink supply nozzle 42a positioned between the two rolls 1, 3a and held in an ink fountain 30 between the rolls 1, 3a. An excess of ink is squeezed from the surface of the anilox roll 1 by the ink squeezing action of the rubber roll 3a.
The printing machines shown in FIGS. 9 and 10 have no need to incessantly recycle the ink to prevent solidification of the ink unlike the flexographic press, therefore require no ink recycling device and can be simplified in construction. The machines further have the advantage that the ink dries fast because of its properties to produce a glossy print surface.
However, the machines described have the following problems. The ink for use in the printing machines of FIGS. 9 and 10, although low in viscosity, has a slightly higher viscosity than the flexographic ink, so that when the excessive ink is scraped off from the anilox roll 1, the ink partly remains unscraped. In other words, the ink adhering to the flat surface of the anilox roll 1 other than the indentations thereof needs to be scraped off by the doctor blade as intended, whereas the slightly higher viscosity is likely to permit a thin layer of ink to remain on the flat surface. Consequently, an excess of ink will be supplied to the printing die on the plate cylinder 2 to give a poor finish to the print. It is also likely that spots of ink as supplied will occur, failing to give a uniform finish to the print. Further when the anilox roll 1 is cleaned for a change of ink, the excessive amount of ink remaining on the roll 1 requires much time and labor for cleaning.
With the printing machine of FIG. 9, the doctor blade 31 provides the ink fountain 30 in cooperation with the anilox roll 1 and is accordingly disposed at an angle so as not to be opposed to the direction of rotation of the roll 1. The doctor blade therefore has a small force (squeezing force) to scrape the ink off the surface of the anilox roll 1. This also allows an excess of ink to be supplied to the printing die on the plate cylinder 2, producing local irregularities in the amount of ink supplied to the printing die.
The amount of ink to be sprayed is adjusted so as not to permit the ink to remain between the anilox roll 1 and the doctor blade 31 to the greatest possible extent. Nevertheless, an amount of ink becomes inevitably collected in the ink fountain 30, so that the change of ink involves the problem that cleaning uselessly washes away the residual ink with the cleaning liquid and requires a prolonged period of time.
In the case of the printing machine of FIG. 10, the rubber roll 3a pressed against the anilox roll 1 is elastically deformed. This results in a reduced ink scraping force, similarly permitting the ink to remain in the flat area of the anilox roll surface.
Further the rubber roll 3a which needs to be provided to the front of the anilox roll 1 gives an increased front-to-rear dimension to the printing machine.
Additionally, the doctor knife 3b bearing on the rubber roll 3a causes earlier damage to the roll 3a.
The ink fountain 30 of the printing machine shown in FIG. 10 also needs to be cleaned of the residual ink. The waste cleaning liquid then remains in the bottom of the ink fountain 30, entailing the drawback that the waste becomes mixed with the ink to be subsequently supplied to the fountain 30.
U.S. Pat. No. 5,265,535 discloses a printing machine for corrugated board sheets which has a doctor blade in contact with the surface of an anilox roll and oriented toward the direction of rotation thereof for controlling the amount of ink on the roll surface. For a change of ink, a scraping blade is brought into contact with the surface of the anilox roll to remove the residual ink, and the roll surface is cleaned by applying a cleaning liquid thereto. This machine is substantially of the same type as those of FIGS. 9 and 10 and has the foregoing problems.